Method and apparatus for making sulphur dioxide



Feb. 9, 1937. I E J MULLEN I 2,070,236

METHOD AND APPARATUS FOR MAKING SULPHUR DIOXIDE Filed March 10 1953 2 Sheets-She t 1 22 v v I El/nu v-gq Fig INVENTOR Edwin d/Vu/lea BY J I ATTORNEY Feb. 9, 1937. MULLEN 2,070,236

METHOD AND APPARATUS FOR MAKING SULPHUR DIOXIDE Filed March 10, 1933 2 Sheets-Sheet 2 INVENTOR Edwin 41 Mullen ATTORNEY Patented Feb. 9, 1937 UNH'ED sm'rss mn'rnon AND APPARATUS non MAKING sULrnUn moms Edwin J. Mullen, New Rochelle, N. Y., asslgnor to General Chemical Company, New York, N. Y., a corporation of New York Application March 10, 1933, Serial No. 660,217

lZClaims.

This invention is directed to methods and apparatus for roasting metallic sulphides, and more particularly for roasting finely divided sulphide ores to desulphurize the same and to produce sulphur dioxide for use in the manufacture of sulphuric acid, or for any other pur- Dose desired. I

Generally speaking, to a large extent the present practice in sulphide fines roasting includes the use of mechanically operated multiple hearth constructions, such, for example, as the well known MacDougal, Herreshofi', and Wedge bumers, and while such burners provide efiective roasting, the complicated construction and operation thereof involve considerable initial and maintenance expense.

As distinguished from the bed roasting operation of these burners, it has been previously suggested to roast the fines while in gaseous sus- .pension, in operations in which the fines are either injected into a roasting chamber in suspension in the oxidizing gas, or are showered downwardly into the roasting chamber wherein the fines encounter cross; or counter currents of suspending gas.

Suspension roasting is best applicable when the fines are in a relatively finely divided state,

' and this method presents the notable advantage over the mechanical multiple hearth operation of considerably lowering the cost of production, by reason of the elimination of the relatively complicated and moving parts, expensive rabbling and other apparatus inherent in the construction and operation of such mechanical bumers. In the practice of suspension roasting, however, and particularly as applied to roasting metallic sulphide fines, difiiculties are encountered which must be overcome before the theoretical advantages of this type of operation are practically available.

some of themore serious operating difliculties arising in connection with suspension roasting of sulphide fines comprise the relatively limited ore capacity of some types of roasters of a given size; in some instances relatively incomplete desulphurization of the fines; comparatively large heat losses by radiation from the extensive surfaces of the roaster exposed to the cooling influences of the atmosphere resulting in more or less inefficient roasting temperatures in the combustion chamber; and the detrimental scar formation on the walls of the roasting chamber. So-called scarring alone, i. e. formation of relatively large bodies of partly desulphurized ore or clinker on the walls of the roasting chamber, causes incomplete desulphurization to a large degree and is a chief source of trouble involving excessive wear and tear on the apps.- ratus, and requiring periodical shut-downs to permit accretions to be manually gouged ofi the furnace walls.

Principal objects of the present invention include the provision of a process for roasting finely divided metallic sulphide fines in suspension by which the capacity of a. given roasting unit may be increased to a large degree, and by which substantially complete oxidation of the metallic sulphides may be readily obtained. The invention further provides for the maintenance of high roasting temperatures in the combustion zone by preventing, to a large extent, heat losses by radiation from the exposed surfaces of the roaster, and the utilization of heat which is conducted or radiated from the combustion 'zone for drying and preheating the sulphide fines. Additionally, the invention presents a method carried out in such manner as to substantially avoid scarring oi the inner walls of the roasting chamber.

Among important features of the present impgivements for roasting metallic sulphides in suspension are utilization of a large amount of radiated or conducted heat to dry and preheat the finely divided moist or wet sulphide fines thus increasing the plant capacity; prevention of heat losses and maintenance of high tempera-- tures in the combustion zone; introduction of the fines at the bottom of the roasting chamber in such manner as to cause the particles to rise to an elevation approaching the top of the chamher, and then permitting the'ore particles to drop back to the base of the roasting chamber to thus provide a path of travel of the fines of maximum length through the roasting chamber, and to maintain the fines in a roasting atmos- 40 phere for a relatively long period of time: Jection of the fines into the roasting chamber and conduct of the roasting operation in such manner as to avoid contact of any. appreciable quantities of ore particles with the walls of'the roasting chamber to overcome scarring of the furnace walls; maintenance of an upwardly moving 0 t of oxidizing gas and withdrawal of the g products of combustion from the top of the roasting chamber, together with control of-t-he velocity and quantity of the upwardly moving gas stream so as to furnish suilicient oxygen to' support the roasting operation, at the same time avoiding contact 01' appreciable amounts of fines with the walls of the roasting 5 movement of the ore particles, a slowing down of the velocity of the fines to zero, and subsequent gravity fall of the fines through the cornbustion zone combined with upward flow of the oxidizing gas stream, thus efiecting a condition in which oxidation of the fines is and completed in an atmosphere rich in oxygen, with intermediate decrease in the rate of travel of the fines to zero thus increasing the time the fines are in the roasting atmosphere.

According to one preferred embodiment, the process of the invention'involves inifial drying and preheating of sulphide fines, by utilization of heat of the top and sides of the roasting furnace, so that relatively large quantities of sulphide fines may be dried and preheated to temperatures promoting rapid ignition on introduction into the roasting zone. The thus dried and preheated fines are run into feed mechanisms positioned at the bottom of the roasting chamber, which mechanisms inject the fines into the roasting chamber either at a relatively high angle or vertically in such manner as to cause the ore particles to rise substantially to the top of the combustion chamber at which point a dispersion of partially roasted fines is formed uniformly over at least the major portion of the area of the top of the roasting zone.

Substantially all of the oxidizing gas, such as air, for supporting the roasting operation is introduced at the base of the burner, preferably either through spaced peripheral openings or 'through the bottom of the combustion chamber,

and rises vertically I through the combustion chamber toward the gas outlet at the top thereof As the ore particles reach the top of the path of travel, the fines, constituting the dispersion of partially roasted material, drop to the bottom of the combustion zone, andwhile falling pass through a stream of oxidizing gas increasingly rich inoxygen. The quantity and velocity of the upwardly directed gas stream are so regulated as to provide suflicient oxygen to effect substantially complete oxidation of theme and to avoid any substantial interference with the free gravity fall of the fines. Conditions are so controlled that at the bottom of the roasting chamber there is a zone consisting of substantially all air and containing little or no sulphur dioxide. In this zone, the incoming, upwardly moving fines are surrounded by an atmosphere rich in oxygen which promotes and hastens ignition of the fines and the beginning of oxidation. The falling, nearly completely oxidized fines, while in this zone, are likewise enveloped in an atmosphere rich in oxygen which facilitates complete oxidation of the hot particles as the latter approach the end of the roasting cycle. The oxide cinder is ultimately discharged from the bottom of the combustion chamber, and sulphur dioxide gases formed during roasting are withdrawn from the top.

The objects and advantages of the invention will be apparent from a consideration of the following description taken in connection with the accompanying drawings, in which Fig. 1 is a vertical section of a preferred burner for carrying out the improved process;

Fig. 2 is a development, on a reduced scale, of an ore heating jacket surrounding the vertical walls of the burner;

Fig. 3 is an enlarged, vertical section of a preferred type of ore feeding mechanism;

Fig. 4 is a vertical section of a burner for chamber and resultant scarring; initial upward carrying out a modified method for roasting sulphide fines; and

Fig. 5 is a vertical section of a modified hopper bottom.

Referring particularly to Fig. l of the drawings, numeral l0 designates generally a shaft burner comprising a shell H constructed of suitable refractory material such as firebrick, and defining a roasting chamber i2 of cylindrical cross-section. Surrounding shell H, is a steel casing i3 acting as a protective reinforcement for the furnace. The upper end of the combustion chamber is closed off by a crown 55, the top side of which forms a drying and preheating hearth H. The cylindrical shell H and casing i3 project upwardly beyond the crown i5, and carry a steel framework i8 which in turn supports ore feeding and rabble mechanism for the drying hearth.

The surface of hearth 8! is slightly coneshaped and slopes downwardly toward the shell of the burner. Lying above the hearth are rabble arms i9 having downwardly projecting plows 20 pitched to work sulphides gradually toward the circumference of the drying hearth.

Arms i9 are rotated by a motor 22 through shaft 23 supported in bearings so as to maintain the lower ends of the plows 20 properly spaced with respect to the surface of the drying hearth ll. An ore bin 2%, mounted on framework !8, discharges ore onto a platform 25 from which fines are intermittently dropped onto approximately the center of hearth W by a sweep 2i rotating with shaft 23.

Surrounding the major portion of refractory wallit and easing I3 is a steel shell joined at the bottom edge with casing i3, forming therewith an ore drying and preheating jacket 32 enveloping a substantial portion of the vertical walls of the burner. Cut in shell Ii. near the upper end, are downwardly sloping passages or conduits 34 through which ore is passed from the drying hearth l'l into the top of jacket 32. The draw ngs show, in section, two of such conduits 33. Preferably several other conduits pass through the top of shell H at spaced points about the circumference of the burner so that, on rotation of the rabble arms l9, ore is gradually fed through such openings 36 into the adjacent parts of the upper end of jacket 32. Placed beneath the lower end of each passage 3% and on the upper edge of jacket 32 are sloping screens 36 which prevent entrance of lumps of ore into the drying jacket 32.

In the embodiment of the apparatus shown in Fig. 1, jacket 32 is provided at the bottom with two diametrically positioned outlets, indicated at 38, through which ore is fed into short pipes 30 having valves 4! for controlling fiow of finely divided ore through pipes 30. The bottom of jacket 32 is formed by four sloping edges Q3, M, 65 and 66 (Figs. 1 and 2), Fig. 2 showing, on a reduced scale, a development of casing 39. Edges 33, M, and M5 of jacket 32 are sloped at an angle greater than the angle of repose of the suphide fines so that the latter run freely to outlets 38 which in turn feed the ore into valve-controlled pipes M3.

The ore injectors comprise principally a metallic pipe section 88, the inner end of. which is set into the shell of the burner at the lower end of the combustion chamber, pipe 08 providing an ore inlet conduit 49. Tube 48 is held in position by a circular plate 58 and a flange 5| bolted to the steel shell I3. The axis of tube 48 is directed upwardly at a relatively sharp angle, and in the particular embodiment of apparatus illustrated, such angle may, for example, be about 75 to the horizontal.

' As shown in Fig. 3 'the valve-controlled pipe 40 projects through the upper side of tube 48. A gas inlet pipe 53 passes through end plate 54, closing the bottom of conduit 49, and terminates at the discharge end of pipe 40. Admission of air or other gas to pipe 53 is controlled by a valve 55. Plug 55 affords means for cleaning out conduit 49 should the same become stopped up.

The burner may be provided with any suitable number of injectors. In the embodiment of the invention, the two injectors shown in Fig. 1 are diametrically disposed. In some instances it is desirable to employ, say, three or more injectors equally spaced about the circumference of the burner. It will be understood where three or more injectors are included in the furnace construction, the configuration of shell 30 is changed accordingly, so as to provide in effect three or more hopper-shaped bottoms terminating in as many outlets 38 for feeding fines into pipes 40. In practice, it is preferred to use three or more injectors to increase the quantity of ore fed to the combustion chamber, and also to increase coverage of the shell II of jacket 32 which covering is greater where the jacket has three or more outlets 38.

Surrounding the burner near the injectors is a bustle 57 for supplying gases to the injector jets 53, the bustle being connected to a gas supply through pipe 58 having therein a control -valve 58'. oxidizing gas to support the roasting operation is introduced into chamber l2 through circumferentially spaced ports 60, positioned adjacent the ore injectors, and connected through short pipe sections, not shown, with bustle 6|, communicating with an air inlet connection, having a control valve therein, and open to the atmosphere, or connected to a fan or blower in case it is desirable to operate the burner under positive pressure. As hereinafter noted, the bustle and short pipe sections may be omitted if desired.

The bottom of the combustion chamber I2 is formed by a hopper-shaped, brick-faced hearth 62 terminating in an outlet 63 through which cinder iscontinuously discharged into a conveyor. As desired, the surface of hearth 62 may be pitched at an angle less or greater than the angle of repose of the cinder as shown for example in Figs. 1 and 5 respectively. This part of the construction of the furnace is referred to hereinafter in connection with the operation of the process. A gas main 64, for withdrawing gaseous products of combustion from the chamber I 2, opens into the latter just beneath the crown I5.

Referring to the modified construction shown in Fig. 4, the burner 65, the top ore drying hearth 66, the rabbling mechanism 61 and the apparatus for rotating" the latter and feeding ore to the drying hearth 66 are substantially the same as described in connection with Fig. 1. The ore drying jacket 69, however, is arranged to provide three hopper-shaped bottoms, only two of which, 10 and 1|, being shown on the drawings. Fines are fed from jacket 69 into outlet pipes 13 and 14, controlled by valves I5 and I6. Pipe I4 discharges fines into one end of a conduit 18, having a screw conveyor 19, which carries the sulphides through conduit I8 and feeds the same into a small funnelshaped hopper into which fines from outlet pipe I3 are also introduced. Connected to the bottom of hopper 80 is pipe 8|, controlled by valve 82, through which ore is charged into inlet conduit 84 having a gas inlet jet 86 regulated by valve 81. Inlet conduit 84 and jet 96 correspond with inlet conduit 49 and nozzle 53 of Fig. 3.

The bottom 90 of the combustion'chamber pitches downwardly toward shell II and is provided in the circumference thereof with one or more cinder outlets 9|. Bottom 90 has a central opening to accommodate a hollow rotatable shaft 92, carrying rabble arms 93 each having a plurality of downwardly extending plows 94 for feeding cinder into openings 9|. The rabble arms 93 are constructed so as to include longitudinal conduits 95, opening into the annular hollow interior of shaft 92, to permit passage through the arms of cooling air which is discharged into the combustion chamber through openings 96. Shaft 92 is supported in suitable bearings, and is rotated by a gear 91 meshing with pinion 98 which in turn is driven from a source of power not shown.

Cooling air is introduced through slots 99, into the annular passage formed in shaft 92 by the vertical section of conduit 84, from an air inlet pipe I00 terminating in a casing I02 surrounding the lower end of the shaft. The quantity of air passing through pipe l00 is controlled by valve I03. Cinder, discharged from the combustion chamber through outlet 9|, runs through pipe I05 into a closed chamber I06 having therein a screw conveyor or other suitable means for discharging cinder without admitting air to the combustion chamber.

As in the modification shown in Fig. 1, substantially all the air required in the process to supply oxygen for the roasting operation is introduced into the combustion chamber through a plurality of ports I01, equally spaced about the shell I I, and opening into the combustion chamber above the surface of the bottom 90, and approximately at the level of the tops of rabble arms 93. Ports I01 communicate through short pipe sections I08 with a circular bustle I09 surrounding the burner. Air is introduced into the bustle through an inlet pipe IIO, controlled by a valve III, connecting with an air main H2.

The invention is applicable to the roasting of divided metal sulphides such as iron pyrites, pyrrhotite, zinc sulphide or arsenopyrlte, but for convenience the operation of the process may bedescribed in connection with the roasting of iron pyrites.

A supply of sulphide fines is maintained in the bin 24 by suitable conveyor or elevator mechanism, not shown. Before roasting is begun, combustion chamber I2 is preheated to temperatures above the ignition point of the particular ore to be roasted, as by the use of oil burners inserted through conveniently located workholes, not shown. Whenthe deslred degree of preheat is obtained in the combustion chamber, the motor 22 is started, and rabble arms I9 and sweep 21 may be rotated at a rate of, say, one revolution in two minutes.- Fines run continuously out of the bin 24 onto platform 25, and on each revolution of shaft 23 a regulated quantity of ore is swept oil the platform -to approximately the center of hearth I1.

During rotation of the rabble arms I 9, the concentrates are gradually worked across the heated surface of hearth ll and into passages 3 3. The dry or partly dry ore runs onto sloping screens 36, which remove lumps, and thence into the top of the drying jacket 32. The finely divided particles gradually drop through the jacket toward outlet-s 38 and into outlet pipes to. Under usual operating conditions jacket 32 may be maintained substantially filled with fines, the gradual downward flow and movement of the particles permitting escape of water vapor formed at the top of the jacket. When roasting is under way, hearth H and the vertical walls of the combustion chamber become relatively highly heated, and the sulphide fines are dried and preheated during movement over the drying hearth H and through jacket 32 surrounding preferably at least a major portion of the burner shell. This operation blankets the .op and sides of the burner with ore which acts as a heat insulator, retaining heat in the combustion chamber, and employing heat which is transmitted to the ore to dry and heat the latter. This preliminary heating serves to dry the fines, thus facilitating the, formation of more satisfactory dispersion of ore in the combustion chamber, and at the same time preheats the fines to temperatures such as to promote ignition shortly after introduction 'into the combustion chamber.

In accordance with the invention, by causing the ore to be roasted to pass over the top and substantially all of the sides of the roasting chamber, a large amount of heat formerly lost to the atmosphere is retained either in the combustion chamber, thus increasing the temperature therein, or is utilized to dry and preheat the fines, and is returned to the combustion chamber in the form of preheat in the ore. Furthermore, inasmuch as the area of heated surface available for drying is largely increased by this procedure, it will be seen that relatively large quantities of ore may be dried and preheated to, say, 300 to 500 F. prior to introduction into the combustion chamber.

Fines ores are usually in a wet or damp condition, containing for example 3-9% water, and hence preferably require drying before roasting by suspension methods. Generally speaking, in prior methods for suspension roasting of fines ore it has been necessary to provide elaborate additional apparatus to dry the ore sufficiently to permit formation of a good suspension in the roasringchamber. By the present method, the wet fines are dried and after drying, preheated to substantially elevated temperatures. It will be seen the capacity of a burner unit of given size is largely increased, inasmuch as one operating limitation of the burner is the amount of ore which can be dried and preheated per unit of time. Although one of the important advantages of the invention lies in the retention in the combustion chamber of reaction heat and utilization of radiated or conducted heat to dry and preheat the ore, roasting, per se, in the combustion chamber does not depend upon drying and preheating, the latter elements relating more particularly to the capacity of the plant than to the roasting operation itself.

Valves 4| in pipes 30 are adjusted so that a substantially steady stream of fines runs into feed conduits 29. The next step of the process involves the injection of the sulphide fines into the combustion chamber. which operation may be satisfactorily effected by use of injectors of the type shown in Fig. 3 of the drawings. Air,

steam, or other gas, not adversely affecting oxidation of .the sulphide, may be employed to charge the fines into the combustion chamber. It is preferred to employ air for this purpose and when using the latter, air may be admitted to the lower ends of conduits 59 through valve controlled jets 53 at pressures of, for example, about 5 pounds per square inch.

If the ore being roasted is of such nature that extraneous fuel is required to maintain proper roasting temperatures, such fuel in any suitable form may be introduced into the combustion chamber through the ore feed mechanism. For example, a combustible gas might be employed to inject the fines.

The particular angle of the'axes of conduits 39 is dependent upon the particular size and type of combustion chamber which may be em ployed. The angle of the axes of conduits 69, the amount of fines fed into the injectors through pipes Ml, andthe air pressure in jets' 53, adjusted by valves 55, are all regulated with respect to the particular size of the roasting chamber so that the ore particles from each injector rise through the combustion chamber, away from the walls thereof, to an elevation just below the underside of crown is. The angular position of conduit 49 and the rate of supply of ore and air thereto are likewise controlled so that the horizontal travel of the ore particles while reaching the top of the combustion chamber and after dropping to the bottom thereof, preferably does not exceed, say, threequarters of the diameter of the roasting chamber. In this manner, contact between any substantial quantities of ore particles and the hot walls of the roasting chamber is prevented, thus avoiding accumulation of scar on the walls. Referring to Fig. 1, the dotted line IM indicates the approximate path of travel of an ore particle of average size introduced through the injector on theleft side of the burner.

Since two or more injectors are preferably employed, the more or less incidental contacting of ore particles constituting the individual streams fed into the combustion chamber by the separate injectors breaks up, to the same degree, the normal paths of travel of the ore particles which would result if a single injector were employed, so that the drop of the fines from the top to the bottom of the combustion chamber is a substantially straight line fall, or one at a high angle. Hence, with respect to the path of travel of fines through the combustion chamber, the ore particles move upwardly at an angle somewhat less than the pitch of injector conduits 49, to an elevation just below crown 15, and then because .of commingling of particles of several individual streams of fines, a relativelyuniform dispersion is formed over a major portion of the upper end of the combustion chamber and thereafter the particles settle in a more or less straight line, at a rate substantially as induced by gravity, toward the hearth in the bottom of the combustion chamber. In this manner, the fines are caused to pass over substantially the longest possible path of travel,

considering the proportions of the combustion chamben It is noted during the latter part of the upward travel of the fine-s, the rate of vertical movement thereof rapidly decreases to zero, and thereafter, during the initial part of the descent of the fines, the rate of downward movement of the fines is relatively small. Hence, while passing upwardly and downwardly through the upper zone of the combustion chamber, the average rate of movement of the fines is low, and this slow rate of travel increases the time the particles are in the roasting atmosphere, thereby giving a relatively long time for the reaction to proceed, thus permitting use of a. roasting chamber of relatively short longitudinal dimension, the roasting of relatively coarse ore, and increased capacity of the burner.

A major portion of the total quantity of air, or other oxidizing gas, necessary to support the oxidization reaction is drawn into the combus tion chamber at the bottom thereof from bustle GI through ports, 60. Where air is employed for injecting the fines through conduits 49, not more than about 10% of the total air required for oxidization would ordinarly be introduced through air jets 53, although larger amounts may be used if desired. In the preferred operation where only a relatively small portion of total air is introduced through the injectors, it may be considered that substantially all the air is introduced into the combustion chamber through ports at the lower end thereof and flows upwardly through the furnace. In the specific embodiment of the invention described, the combustion chamber is about l6 feet high and of about the same diameter. While such particular proportion of the roasting chamber is preferred, it is to be understood that the diameter of the chamber may, in some instances advantageously exceed the height by a substantial amount, and may also be somewhat less than the height. Preferably the diameter of the chamber is not less than the height. Since the combustion chamber preferably has a large diameter per unit of volume, it will be seen that the velocity of the upwardly flowing stream of oxidizing gas may be held at a minimum As noted, the sulphides, preheated to, say, 300-500 F., are injected into the bottom of the combustion chamber, and as all the air for oxidation is drawn in through ports 60, and some through cinder-outlet 63, it will be seen the fines are initially charged into an atmosphere rich in oxygen. In operation, it has been noted a relatively clear atmosphere exists in about the lower 30-48 inches of the vertical height of the combustion chamber, thus indicating the existence of a zone of relatively pure air, containing at the most but little sulphur dioxide. Although the atmosphere at and just above the ends of the inlet conduits 49 is relatively cool because of the introduction of air through ports W at about atmospheric temperature, the heating of 'the upward moving ore particles to the ignition temperature takes place rapidly, owing to absorption of heat from falling roasted particles,

which in this particular zone, are at tempera Observations show that" tures of incandescence. the ore particles are raised to the ignition temperature within a distance between 10 and 24 inches from the ends of conduits fig. Thus, transfer of heat from the falling. incandescent roasted particles and, the presence of an atmosphere rich in oxygen, together serve to bring about ignition of fines shortly after introduction into the base of the combustion chamber.

Following ignition, the fines to approximately the top of the combustion chamber, the temperature of the particles increasing because of rapidly progressing roasting. Although the air introduced through ports 60 is initially at about normal temperatures, the roasting operation is such that the temperature of the roasting atmosphere increases at a relatively uniform rate until the temperature of the gases in the top of the roasting chamber, on entering outlet 84, may be about 1800-2000 F. Conduit 64 is connected to the inlet side of a blower so that the burner operates under a slight negative pressure. In some instances, bustle 6| may be omitted, and air drawn in directly from the atmosphere, although omission of the bustle and the valve-controlled inlet pipe thereof obviate to some extent, flexibility of control of the amount of air entering through ports 60. If it should be desired to use preheated air, such may be introduced through bustle 69.

At the uppermost point oftravel of the fines, a relatively uniform distribution of partially roasted particles is formed over the major portion of the upper end of the combustion zone and the downward movement of the particles begins. The latter thereafter drop through the combustion chamber at a rate substantially the same as that. of similar' particles falling under the influence of gravity. In the preferred mode of operation, the blower in gas line 64 is operated so as to supply suflicient' oxygen to effect substantially complete oxidation of the fines and also in such manner that the velocity of the rising stream of air through the combustion chamber is not sufficient to interfere with the free gravity fall of the fines. Because of the angular pitch of inlets 49, and other above-noted control conditions, ore particles during the upward movement are not thrown against thewalls of the roasting chamber, and thus avoid contact of fines with the hot walls of the combustion chamber when the fines are in a state conducive to scarring. As the'downward flow of the fines is in substantially straight lines or at a high angle, subsequent contact of fines with the walls of the combustion chamber is avoided, thus further preventing conditions under which scarring might take place.

At the time downward movement of the ore particles begins, roasting is well under way, but because of the decreased sulphur content of the fines, further oxidation and removal of the residual sulphur proceed with'less ease. To complete roasting, it is therefore desirable to cause the ore particles to pass through an atmosphere increasingly rich in oxygen and containing less sulphur dioxide. In the operation of the present process, this condition is present, and as the fines fall freely, they drop through an atmosphere increasingly rich in oxygen, until in a zone of approximately 38-48 inches depth in the bottom of the furnace, the ore particles pass through an atmosphere of substantially pure air. During fall of the fines, the temperature of the particles increases, promoting oxidation, and as the particles enter the lower zone, scintillation of the individual particles may be observed, thus indicating oxidation of iron and temperatures of the iron oxide particles in the neighborhood of 2000-2600 F. The ironoxide cinder falling on hopper-shaped hearth 62 is finely divided, free-flowing, and runs through opening 63 into a suitable conveyor. As above noted, conditions are such in the combustion chamber that there is a slight negative pressure at opening 63, the small amount of air drawn in being utilized for oxidation.

In the furnace of Fig.1, the pitch of the surface of hearth 62 may be considered, for example, as being less than the angle of repose of, the

cinder. In this instance, a layer of cinder will buildiip on the hearth, the surface of the cinder layei being indicated approximately by dotted line its. in the modification of Fig, 5, it may be considered the pitch of the surface of hearth 62 is greater than the angle of repose of the cinder. When the latter construction is employed, the lower edge of the hearth may be provided with a circular vertical flange MS of such height as to maintain a layer of cinder covering the surface of hearth 62. In Fig. 5, the dotted line ill represents the upper surface of a bed of cinder, lying at the angle of repose on the hearth, and covering substantially the entire surface of the hearth.

It will be seen in a construction of both Figs. 1 and 5, there is maintained a layer of cinder of appreciable thickness covering substantially the entire surfaces of hearths 62. As the cinder in the hearth may be at temperatures of for example 1400-1600 F., the presence of a layer of hot cinder on the furnace hearth is a material factor in maintaining high temperatures and satisfactory roasting conditions in the combustion chamber.

The injector mechanism shown in Fig. 1, together with the particular method of introducing the sulphide fines at spaced points about the periphery of the base of the combustion chamber have been illustrated for the purpose of showing preferred and satisfactory ways of carrying out the roasting operation. However, other methods of introducing the ore in the bottom of the combustion chamber may be employed. For example, the fines may be injected into the combustion chamber either centrally or peripherally by suitable mechanical devices. Another example is shown in the embodiment illustrated in Fig. 4. When operating with such apparatus, the fines from jacket 69 are fed into the hopper through pipe 73, and pipe M and conduit it. The dried and preheated fines then run through pipe 8! corresponding with ore inlet 40 of Fig. 3. As in the operation of the apparatus in Fig. 1, air is admitted to conduit 8 (Fig. 4) through jet to controlled by valve 817, the amount of air being limited to thatsuiiicient to carry the ore particles through conduit 86 to the nozzle 8 and thence to approximately the top of the combustion chamber. The roasting operating taking place in the combustion chamber of the apparatus of Fig. 4 involving therise of the ore particlesto the top of the combustion chamber and the subsequent fall to hearth 90 is substantially the same as already described relative to Fig. l.

In Fig. 4 the cinder falls onto the bottom 90, and the lower ends of plows 94 and rabble arms 93 are so adjusted as to facilitate the maintenance on the bottom of the combustion chamber of a bed of cinder of appreciable thickness, say, 2 to 4 inches. As the area of the cinder bed is relatively extensive and the temperature of the cinder being around say 1400-1600" F., large quantities of heat are radiated from the cinder bed upwardly into the combustion zone. The advantages described above relative to the maintenance of a cinder layer in the bottom of the combustion chamber are obtained in the operation of a burner of the type shown in Fig. 4. The burner may be operated at a slight positive pressure, and under conditions such that the velocity of the upwardly flowing stream of oxidizing gas-in the combustion chamber is substantially the same as in the operation of the the art. Gases containing apparatus of Fig. l. Rabble arms 93 are rotated at a suitable rate, and cinder is ultimately discharged from the bottom of the combustion chamber through one or more air-locked outlets I05. If it should be desired to introduce preheated air through ports I01, such air may be preheated by heat transfer from hot cinder after discharge of the latter from the combustion chamber.

The sulphur dioxide gases produced may be used, for example, in the manufacture of sulphuric acid. The sulphur dioxide content of the burner gas may be regulated as desired by adjusting the'amount of air fed into the combustion chamber as is known by those skilled in l0l5% sulphur dioxide may be readily made by the present process.

The invention presents numerous advantages relative to increased capacity of the burner,

desulphurizatibn of the fines, retention of heat in the combustion zone, and prevention'of scarring on the walls of the combustion chamber.

With particular reference to oxidation of the fines, it is to be noted that by injectingthe ore in the air zone at the bottom of the burner the sulphide is brought rapidly to the kindling temperature by heat absorption from the glowing iron oxide. Further, the final heating of the fines to ignition temperature is not dependent upon the burning of the free atom of sulphur contained in the ore particles. By reason of this, it is readily possible to efficiently roast in suspension ores such as pyrrhotite containing less sulphur than sulphides such as iron pyrites. Additionally, the ore particles pass over a path of substantially maximum length, which retains the fines in a roasting atmosphere for a long period of time, brings about more complete desulphurization of the ore, and increases the capacity of the furnace, while permitting use of a combustion chamber of relatively limited vertical dimension. Movement of fines and glowing iron oxide in heat exchange relationship in the lower end of the furnace fi6CtS filcient transfer of heat from the hot cinder oxide particles to the incoming ore. The atmosphere in the bottom of the combustion zone, into which the fines are initially introduced, is rich in oxygen which together with heat transfer from the hot iron oxide to incoming ore causes rapid ignition of the latter. In the first stage of roasting there is an atmosphere rich in oxygen which greatly aids in starting oxidation, and in the later phase, there is provided an atmosphere increasingly rich in oxygen which facilitates complete desulphurization of the fines at a stage in which oxidation tends to slow down.

Regarding increased sulphur dioxide gas production of a unit of given size made possible by the present process, the greater cre drying and preheating capacity resulting from absorption of radiated heat from the top and sides of the combustion chamber, and utilization of the fines as an insulating blanket raises the capacity of the burner considerably in excess of that obtainable where drying is limited to a single hearth such as hearth H. Hence, with respect to fines of a given moisture content, the

production of the burner may be increased, or when a wetter ore is to be roasted, the same capacity as heretofore may be obtained. It is also possible to obtain a greater preheat of a given amount of ore, or the same preheat as heretofore of a larger quantity of ore. By casing the vertical walls of the burner shell with ore drying and preheating jackets, the insulating efiegt of the ore blanket prevents heat losses fro the roasting zone, thus helping to increase and maintain at higher temperatures'the heat prevailing in the combustion chamber.

As previously noted, oxidizing gas rising from the bottom to the top of the combustion chamher flows at such velocity as to cause no appre-v ciable interference with free fall of the ore particles, avoiding contact of fines with the hot walls of the combustion chamber and consequent scar formation which, in suspension roasting operations, is a recognized substantial detriment.

In the above description and in the appended claims, the term fines is intended to designate material of such degree of subdivision as may be roasted while suspended in oxidizing gas, one. of the further advantages of the invention being that, by the process thereof, relatively coarse material, for example 35 mesh pyrrhotite may be roasted.

I claim:

1. The method of roasting finely divided metallic sulphides to produce sulphur dioxide which comprises passing fines to be roasted in heat exchange relation with the top and at least a major portion of the sides of a heated combustion zone whereby fines are dried and preheated, and heat loss from the combustion zone prevented, injecting the fines into the bottom of the combustion zone at the periphery thereof, further heating the fines by heat absorption from roasted cinder, passing the fines upwardly then downwardly through the combustion zone over substantially the longest path of travel, flowing a stream of oxidizing gas upwardly through the combustion ,zone, regulating the quantity and velocity of the stream of oxidizing gasto provide sufiicient oxygen to eifect substantially complete oxidation of the fines and avoid interference with the free gravity fall of the particles through the combustion zone, discharging cinder from the bottom of the combustion zone, and withdrawing sulphur dioxide containing gases from the top of the combustion zone.

2. Apparatus for roasting finely divided metallic sulphides comprising a shell forming a substantially cylindrical, vertically disposed com.- bustion chamber having a relatively horizontal top, a jacket surrounding at least a major portion of the shell, said jacket extending adjacent the lower end of the shell and having outlets at the bottom thereof, means for feeding finely divided sulphides onto the center of the top, means for wormng the fines gradually over the surface of the top toward the periphery of the shell and into the upper end of the jacket, a plurality of ore feeding conduits spaced about the periphery of the shell adjacent the base thereof, said conduits being inclined at a relatively high angle to the horizontal and opening into the combustion chamber at points higher than the inlet ends of the ore feeding conduits, means for feeding ore from the outlets in the bottom of the jacket into the feed conduits to charge ore intothe combustion chamber, a plurality of gas inlet ports spaced about the periphery adjacent to the base of the shell, means for discharging cinder from the bottom of the combustion chamber, and a gas outlet at the top for withdrawing gaseous products oi:

to produce sulphur dioxide which comprises introducing sulphide fines near the base portion of a substantially unobstructed combustion chamber heated to temperature above the ignition point of the fines and having a. large horizontal dimension relative to the height, passing the fines upwardly and then downwardly over a distance approaching the vertical dimension of said combustion chamber so as to cause the fines to move through an extended path and to prevent contact of any substantial quantities of fines with the heated walls and top of said combustion chamber, separately introducing an oxygen-containing gas into the combustion chamber in proximity to the point of introduction of the fines, flowing the oxygen-containing gas at velocity less than the initial velocity of the fines and such as to substantially avoid interference with gravity fall of the fines, in upward direction only through substantially the whole of the combustion chamber in countercurrent flow to the downwardly flowing fines so that the downwardly flowing fines pass through a roasting atmosphere increasingly rich in oxygen, and withdrawing sulphur dioxide containing gases from the top portion of the combustion chamber.

4. The method of roasting metal sulphide fines to produce sulphur dioxide which comprises introducing sulphide fines at the lower periphery of a. substantially unobstructed combustion chamber heated to a temperature above the ignition point of the fines and having a large horizontal dimension relative to the height, passing the fines upwardly and then downwardly over a distance approaching the vertical dimension of said combustion chamber so as to cause the fines to move through an extended path and to prevent contact of any substantial quantities of fines with the heated walls and top of said combustion chamber, separately introducing an oxygen-containing gas into the combustion chamber in proximity to the point of introduction of the fines, flowing the oxygen-containing gas, at velocity less than the initialvelocity of the fines and such as to substantially avoid interference with gravity fall of the fines, in upward direction only through substantially the whole of the combustion chamher in countercurrent flow to the downwardly flowing fines so that the downwardly flowing fines pass through a roasting atmosphere increasingly rich in oxygen, and withdrawing sulphur dioxide containing gases from the top portion of the combustion chamber.

5. The method of roasting metal sulphide fines to produce sulphur dioxide which comprises introducing sulphide fines at the lower periphery and in a direction away from the adjacent wall of a substantially unobstructed combustion chamber heated to a temperature above the ignition point of the fines and having a large horizontal dimension relative to the height, passing the fines upwardly and then downwardly and over a distance approaching the vertical dimension of said combustion chamber so as to cause the fines to move through an extended path and to prevent contact of any substantial quantities of fines with the heated walls and top of said combustion chamber, separately introducing an oxygen-containing gas into the. combustion chamber in proximity to the point of introduction of the fines, flowing the oxygemcontaining gas upwardly through the combustion chamber with upwardly moving fines at velocity less than the initial velocity of the fines and such as to substantially avoid interference with gravity fall 6. The method of roasting metal sulphide fines to produce sulphur dioxide which comprises introducing sulphide fines into the base portion of a substantially unobstructed combustion chamber heated to a temperature above the ignition point of the fines and having a large horizontal dimension relative to the height, said fines being injected into the combustion chamber so as to cause at least a. substantial portion of the fines to travel upwardly and then downwardly through substantially the height of said combustion chamber and to cause at least a substantial portion of the fines to move over substantially the longest path of travel and remain in the roasting atmosphere for a maximum period of time and to prevent contact of any substantial quantity of fines with the heated walls of ,the combustion chamber, separately introducing a stream of oxidizing gas moving at velocity less than that of initial velocity of the fines into the base portion ofthe combustion chamber, passing said stream of oxidizing gas in upward direction only through substantially the whole of the combustion chamber in countercurrent fiow relation to the downwardly fiowing fines so that the downwardly'fiowing fines pass through a roasting atmosphere increasingly rich in oxygen. regulating the quantity and volume of said upwardly flowing gas stream so as to provide sumcient oxygen to efiect rela tively complete oxidation of the fines and to avoid causing contact of any substantial quantity of fines with side walls and top of the combustion chamber and to substantially avoid interference with gravity fall of the fines, maintaining said combustion chamber at temperature above the ignition point of the fines after combustion of the fines has once commenced solely by combustion of said fines, withdrawing sulphur dioxide gases from the top of the combustion chamber, and discharging cinder from the lower end thereof.

7. The method of roasting metal sulphide fines to produce sulphur dioxide which comprises introducing sulphide fines near a side wall and also the base portion of a substantially unobstructed combustion chamber heated to a temperature above the ignition point of the fines and having a large horizontal dimension relative to the height, said fines being injected into the combustior chamber in a. direction away from said wall and so as to cause at least a substantial portion of the fines to travel upwardly and then downwardly through substantially the height of said combustion chamber and to cause at least a. substantial portion of the fines to move over substantially the longest path of travel and remain in the roasting atmosphere for a maximum period of time, and to prevent contact of any substantial quantity of fines with the heated walls of the combustion chamber, separately introducing a. stream of oxidizing gas moving at velocity less than that of the initial velocity of the fines into the base portion of the combustion chamber, passing said stream of oxidizing gas in upward direction only through substantially the whole of the combustion chamher in countercurrent fiow relation to the down wardly flowing fines so that the downwardly flowing fines pass through a roasting atmosphere increasingly rich in oxygen, regulating the quantity and volume of said upwardly flowing gas stream so as to provide sufiicient oxygen to effect relatively complete oxidation of the fines and to avoid causing contact of any substantial quantity of fines with side walls and top of the combustion chamber and to substantially avoid interference with gravity fall of the fines, maintaining said combustion chamber at a temperature above the ignition point of the fines after combustion of the fines has once commenced solely by combustion of said fines, withdrawing sulphur dioxide gases from the top of the combustion chamber, and discharging cinder from the lower end thereof.

8. The method of roasting metal sulphide fines to produce sulphur dioxide which comprises introducing sulphide fines at the periphery of the base portion and in a direction away from the adjacent wall of a substantially unobstructed combustion chamber heated to a temperature above the ignition point of the fines and having a large horizontal dimension relative to the height, said fines being injected into the combustion chamber so as to cause at least a substantial portion of the fines to travel upwardly and then downwardly through substantially the height of said combustion chamber and to cause at least a substantial portion of the fines to move over substantially the longest path of travel and remain in the roasting atmosphere for a maximum period of time, and to prevent contact of any substantial quantity of fines with the heated walls of the combustion chamber, separately introducing a stream of oxidizing gas moving at velocity less than that of the initial velocity of the fines into the base portion of the combustion chamber, passing said stream of oxidizing gas in upward direction only through substantially the whole of the combustion chamber in countercurrent fiow relation to the downwardly fiowing fines so that the downwardly fiowing fines pass through a roasting atmosphere increasingly rich in oxygen, regulating the quantity and volume of said upwardly flowing gas stream so as to provide sufiicient oxygen to effect relatively complete oxidation of the fines and to avoid causing contact of any substantial quantity of fines with side walls and top of the combustion chamber and to substantially avoid interference with gravity fall of the fines, maintaining said combustion chamber at a temperature above the ignition point of the fines after combustion of the fines has once commenced solely by combustion of said fines, withdrawing sulphur dioxide gases from the top of the combustion chamber, and discharging cinder from the lower end thereof.

9. The method of roasting metal sulphide fines to produce sulphur dioxide which comprises introducing sulphide fines at the periphery of the base portion of a substantially unobstructed combustion chamber heated to a temperature above the ignition pointof the fines and having a large horizontal dimension relativeto the height, said fines being injected into the combustion chamber by means ofa stream of air under superatmospheric pressure in a direction away from the adjacent side wall so as to cause at least a substantial portion of the fines to travel upwardly and then downwardly through substantially the height of said combustion chamber and to cause at least a substantial portion of the fines to move over substantially the longest path of travel and remain in the roasting atmosphere for a maximum period of time, and

to prevent contact of any substantial quantity of fines with the heated walls of the combustion chamben'separately introducing a stream of oxidizing gas moving at velocity less than that of the initial velocity of the fines into the base portion of the combustion chamber, passing said stream of air in upward direction only through substantially the whole of the combustion chamber in countercurrent flow relation to the downwardly fiowing fines so that the downwardly flowing fines pass through a roasting atmosphere increasingly rich in oxygen, regulating the quantity and volume of said upwardly flowing air stream so as to provide sufficient oxygen to effect relatively complete oxidation of the fines and to avoid causing contact of any substantial quantity oi fines with side walls and top of the combustion chamber and to substantially avoid interference with the gravity fall of the fines, maintaining said combustion chamber at a temperature above the ignition point of the fines after combustion of the fines has once commenced solely by combustion of said fines, withdrawing sulphur dioxide gases from the top of the combustion chamber, and discharging cinder from the lowerend thereof.

10. The method of roasting metal sulphide fines to produce sulphur dioxide which comprises introducing sulphide fines at the lower periphery and in a direction away fromthe adjacent wall of a substantially unobstructed combustion chamber heated to a temperature above the ignition point of the fines and having a large horizontal dimension relative to the height, said fines being injected into the combustion chamber so as to cause a major portion of the fines to travel upwardly and then downwardly through substantially the height of said combustion chamber and to cause the fines to move over substantially the longest path of travel and remain in the roasting atmosphere for a maximum period of time, and to prevent contact of any substantial quantity of fines with the heated walls of the combustion chamber, separately introducing a stream of oxidizing gas moving at velocity less than that of the initial velocity of the fines into the base portion of the combusttion chamber, passing said stream of oxidizing gas upwardly through the combusion chamber with the upwardly flowing fines, regulating the quantity and volume of said upwardly flowing gas stream so as to provide sufliclent oxygen to effect relatively complete oxidation of the fines and to avoid causing contact of any substantial quantity of fines with heated side walls and top of the combustion chamber and to substantially avoid interference with the gravity fall of the commenced solely by combustion of said fines, withdrawing sulphur dioxide gases from the combustion chamber, and discharging cinder 'from the lower end thereof.

11. The method of roasting metal sulphide fines to produce sulphur dioxide which comprises introducing suphide fines at the lower periphery of a substantially unobstructed combustion chamber heated to temperature above the ignition point of the fines and having a large horizontal dimension relative to the height, passing the fines upwardly in a direction having a substantial horizontal component and then downwardly over a distance approaching the vertical dimension of said combustion chamber so as to cause the fines to move through an extended path and to prevent contact of any substantial quantities of .fines with the heated walls and top of said combustion chamber, separately introducing an oxygen-containing gas into the lower end of the combustion chamber, flowing the oxygen-containing gas at velocity less than the initial velocity of the fines and such as to substantially avoid interference with gravity fall of the fines, in upward direction only thru substantially the whole of the combustion chamber in countercurrent flow to the downwardly flowing fines so that the downwardly flowing fines pass thru a roasting atmosphere increasingly rich in oxygen, and withdrawing sulphur dioxide containing gases from the top portion of the combustion chamber.

12. The method of roasting metal sulphide fines to produce sulphur dioxide which comprises introducing sulphide fines near the base portion of a substantially unobstructed combustion chamber heated to temperature above the ignition point of the fines and having a large horizontal dimension relative to the height, passing the fines upwardly and then downwardly over a distance approaching the vertical dimension of said combustion chamber so as to cause the fines to move through an extended path and to prevent contact of any substantial quantities of fines with the heated walls and top of said combustion chamber, separately introducing an oxygen-containing gas into the lower end of the combustion chamber, flowing the oxygen-containing gas at velocity less than the initial velocity of the fines and such as to substantially avoid interference with gravity fall of the fines, in upward direction only through substantially the whole of the combustion chamber in countercurrent fiow to the downwardly flowing fines so that the downwardly flowing fines pass through a roasting atmosphere increasingly rich in oxygen, and withdrawing sulphur dioxide containing gases from the top portion of the combustion chamber.

EDWIN J. MULLEN. 

